This invention relates to the postcrosslinking of pendant vinyl groups of crosslinked macroporous copolymers to produce macroporous adsorbents with improved properties. In particular the present invention relates to the use of organic sulfonic acids to provide the postcrosslinking of the macroporous copolymers.
High surface area adsorbents can be prepared by the "macronetting" of divinylbenzene copolymers or by the suspension polymerization of divinylbenzene (DVB) in the presence of a nonsolvent. These high surface area adsorbents are useful for the removal of organics from non-organic streams and have found use in a wide variety of applications including the removal of organic wastes from water and the recovery of pharmaceutical products from fermentation broths.
"Macronetted" or "hyper-crosslinked" adsorbents represent one class of adsorbents and can be produced by postcrosslinking involving the introduction of alkylene-bridge crosslinks into a swollen copolymer subsequent to initial polymerization, as described in U.S. Pat. Nos. 4,191,813, 4,263,407, 5,416,124 and D. A. Davankov et al., Reactive Polymers, Elsevier Science Publishers, Vol. 13, pages 27-42 (1990). The process disclosed in U.S. Pat. No. 4,191,813 involves first swelling a crosslinked vinylbenzylchloride-containing copolymer with an organic solvent followed by treatment with a Lewis-acid catalyst. The process described in U.S. Pat. No. 4,263,407 involves first swelling a crosslinked polystyrene copolymer with an organic solvent followed by treatment with a Lewis-acid catalyst in the presence of a polyfunctional Friedel-Crafts-reactive crosslinker. In both cases, upon heating the reactants, the substrate copolymer aromatic rings are further crosslinked (macronetted) with methylene or alkylene-type "bridges" derived from the chloromethyl group or reactive polyfunctional crosslinker. Another well-known approach to prepare macronetted adsorbents is first to chloromethylate a styrene/DVB copolymer with chloromethyl ether and then form methylene bridge crosslinks by adding a Friedel-Crafts/Lewis-acid catalyst in the presence of a swelling solvent (see U.S. Pat. No. 5,416,124 and Davankov et al.).
Macronetted adsorbents produced as described above swell in organic solvents and have been found to be less structurally stable than conventional "non-macronet" polydivinylbenzene adsorbents, the latter, for example, being represented by highly crosslinked polymers prepared by suspension polymerization in the presence of a nonsolvent. Additionally, the production of these macronetted adsorbents requires the use of organic swelling solvents and Friedel-Crafts/Lewis-acid catalysts that are difficult to remove from the final product.
Macroporous copolymers produced from the suspension polymerization of DVB-containing monomer mixtures in the presence of a nonsolvent represent another class of adsorbents with a particular pore size distribution and surface area (conventional macroporous adsorbents). These conventional macroporous copolymers often contain a significant amount of pendant vinyl groups resulting from the incomplete crosslinking of DVB (R. V. Law et al., Macromolecules, Vol. 30, pages 2868-2875 (1997); K. Lise Hubbard et al., React. Funct. Polym, Vol. 36 (1), pages 17-30 (1998)). The incomplete crosslinking of these vinyl groups leads to a material with undesirable swelling properties in organic solvents, such as solvents used during adsorption/regeneration operations. Additionally the unreacted vinyl groups represent a potential site of undesirable chemical reactivity.
The enhancement of surface area and porosity of crosslinked macroporous copolymers by postcrosslinking the pendant vinyl groups has been disclosed in U.S. Pat. No. 5,218,004, where enhanced surface area was achieved by reacting the residual vinyl groups of a crosslinked copolymer (preconditioned with swelling solvent) with a Lewis-acid catalyst in the presence of water or other nonswelling liquid at elevated temperature. U.S. Pat. No. 4,543,365 discloses the use of a Lewis-acid catalyst to increase the surface area of a copolymer containing 8 to 80 percent crosslinker by postcrosslinking in the presence of an organic swelling agent.
The problem addressed by the present invention is to overcome the deficiencies of prior methods used to prepare high surface area adsorbents, such as requiring the use of swelling solvents and Lewis-acid/Friedel-Crafts catalysts, and to provide high surface area macroporous adsorbents having improved swelling properties, that is, a reduced tendency to swell in solvents during the adsorption/regeneration cycles of typical end use applications.